In general, a vacuum circuit breaker is widely used in electrical equipment in substations or in distribution systems on account of its capability in interrupting a large current with a small sized structure. The construction of a main body of bulb in a vacuum circuit breaker is such that a set of a fixed electrode fixed at the end of face of a current-carrying conductor and a moving electrode fixed similarly on the end face of another current-carrying conductor disposed facing each other is accommodated in an insulative vacuum tube of ceramic or similar material kept vacuum. The main body of bulb is used in a vacuum circuit breaker, being installed in an atmospheric environment or in an insulating gas atmosphere, wherein an operating device is provided near the main body of bulb to manipulate the moving electrode.
The operating device used in a vacuum circuit breaker causes the open-close motion between the moving electrode and the fixed electrode, wherein the operating device converts turning movement of a rotating shaft into a linear motion through a mechanism provided therein such as a lever to make the moving electrode move linearly. That is in particular; the operating device opens the moving electrode separating it from the fixed electrode on receipt of an open command from a control unit to interrupt current and closes these electrodes on receipt of a close or a reset command from the control unit; the operating device further provides a spring such as a compression-spring or a wipe spring for such motion.
The compression-spring or a device for similar purpose is used: to ensure a smooth operation of the moving electrode for opening and closing, to apply a predetermined magnitude of contact pressure over the moving and the fixed electrodes on completion of the closing operation, and to prevent a bouncing in the closing motion of the moving electrode to the fixed electrode that may damage the contact faces of the electrodes.
JP08-298040A1 (Patent Literature 3) has proposed an example of vacuum circuit breaker that uses a compression-spring or the like such as a pressing-spring. This vacuum circuit breaker has such a operating device that a lever, which operates a current-carrying conductor of a moving electrode, is fixed on a rotating shaft thereof and that the rotating shaft has a cam device at its top end. In this mechanism, a pressing-spring is arranged on the extended line of the current-carrying conductor of the moving electrode, wherein one end of the pressing-spring engages with the cam device. Thereby; while the lever moves from the electrodes-open position to the electrodes-close position, the cam device compresses the pressing-spring to store pressing energy for applying pressure; while in contrast the lever moves from the electrodes-close position to the electrodes-open position, the cam device allow the pressing-spring to release the stored pressing energy gradually.
Another example of vacuum circuit breaker that JP06-103863A1 (Patent Literature 2) has disclosed such a configuration that a motion converting mechanism is connected to the rotating shaft of a operating device through a lever so that this conversion mechanism will convert a horizontally reciprocating motion into a vertically reciprocating motion to operate a current-carrying conductor to which a moving electrode is fixed. At the bottom end of an insulative manipulating rod arranged on the extended line of the current-carrying conductor of the moving electrode, a wipe spring is installed to mediate a smooth operation of the close-open movements of the moving and fixed electrodes.
It is a common feature to the circuit breakers described in Patent Literatures 1 and 2 that each of them has single pressing-spring in its lever- or operating-mechanism. An intention of gaining a smooth close-open operation in the moving electrode relying on a single pressing-spring operating device encounters a ceiling.
Employing the single pressing-spring style involves a difficulty in the adjusting of the pressing force to a proper contact pressure on a set of moving and fixed electrodes; inadequate spring pressure of the pressing-spring does not give a proper assisting force to the operation of the operating device. FIG. 5 indicates a stroke characteristic of moving electrodes in terms of time, wherein T represents the time-elapse for movement of the moving electrode and St the traveling stroke of the electrode. As shown in the figure, the time-stroke characteristic of a moving electrode in a conventional vacuum circuit breaker behaves as given a time-stroke characteristic curve of S1.
That is: the moving electrode in a conventional vacuum circuit breaker moves linearly at a constant rate of move both in the opening-stage and the closing-stage, wherein the opening-stage is a period from the time point To (shown on the left side in the diagram), at which the opening motion starts, to the time point To1 at which the opening motion ends, and the closing-stage is a period from the time point Te (shown on the right side in the diagram), at which the closing motion starts, to the time point Te1 at which the closing movement ends.
This time-stroke characteristic prevents an improved interruption characteristic since operating the moving electrode through a operating device working on a single pressing-spring cannot produce a higher initial opening speed. Further, the single spring mechanism cannot produce a reduced closing speed of the moving electrode, which causes the impact energy E (=kmv2), given by a constant k, the mass m, and the collision speed v of the moving electrode, to become large. Such larger energy easily causes bouncing between the contact faces of the moving and the fixed electrodes developing into such a problem as invites a serious contact face damage.
Consideration of such problem desires vacuum circuit breakers should gain an extended service lifetime by the use of such a compression-spring as will improve interruption performance reducing contact face damage of a moving and a fixed electrodes to which bouncing is responsible with improved voltage withstand performance between electrodes and enhanced interruption performance.
An advantage of the present invention is to provide a vacuum circuit breaker that offers an extended service lifetime rendered by an increased initial opening speed of a moving electrode with an improved interruption performance, a reduced contact face damage on a moving and a fixed electrodes, and an improved voltage withstand performance between electrodes and enhanced interruption performance.